Thermostatic discharge tube



March 31, 1942. I

H. J. McCARTHY 2,277,708

THERMQSTATIC DISCBARGE TUBE Filed March 18, 1940' ATTORNEY Patented Mar. 31, 1942 THERMOSTATIC DISCHARGE TUBE Henry J. McCarthy, Danvers, Mass, assignor to Hygrade Sylvania Corporation, Salem, Mass, a corporation of Massachusetts Application March 18, 1940, Serial No. 324,533

1 Claim.

This invention relates to the apparatus necessary for the proper operation of electric gaseous discharge lamps.

An object of the invention is to provide switch ing means by which the cathodes of said lamps may be pre-heated to the degree of heat necessary to facilitate the starting of the main discharge.

Other objects are to provide switching means so timed in action that sufiicient time is provided for the proper pre-heating of the cathodes of the lamp under all possible conditions of starting and re-starting and which takes no appreciable power after the lamp has started. Thus a greater efiiciency is provided in this switch over those now in use in the art.

Some of these now in use, because of their peculiar structure require a certain amount of current through the switch at all times when the lamp is running whereas the switch in this invention is constructed so that practically no current flows through it once the cathodes have been properly pre-heated.

Figure 1 is a diagram of the arrangement of apparatus according to the invention.

Figure 2 is a side view of the switching device according to the invention.

In Figure 1, a gaseous discharge lamp l, comprises a sealed glass envelope 2, with an electrode 3 at each end of the tube, each electrode comprising a coil or wire, preferably tungsten, bearing an electron emitting coating, such as a coating of the alkaline earth oxides. The tungsten coil is preferably of the coiled-coil or doubly coiled type in order to hold more efiiciently the oxide coating, and to provide a higher voltage drop across the cathode at starting, than would a singly coiled electrode.

Lead-in wires 4, 5, 6, and I extend from the ends of the coils through the ends of the glass envelope 2, to act as contacts to the remainder of the apparatus. The tube contains an atmosphere of inert gas, such as argon. Lead-in wire 6 is connected to one end of the power line from which the lamp is operated. This power line may conveniently have a voltage of 220 volts. At the other end of the lamp, lead-in wire 4 is connected to the other side of the power line through the reactance coil 8. Lead-in wires 5 and 1 may be connected through the contacts 9 and I0 and the bimetallic strip II in the switch [2, which is a sealed envelope containing an atmosphere or an inert gas, say neon, at a low pressure say 8 mm. The bimetallic strip is permanently fixed to contact point 9 and is so spaced from contact contact points 9 and I0.

point ID that a discharge occurs through the gas, when the circuit is connected to the line, the discharge heating the strip enough to close the The short circuit thus created will cause the current passing through the electrodes 3 to heat them to a point sufiicient to start the discharge in the lamp. This proper heating point is reached at approximately the same time that the bimetallic strip II, which has been cooling since it established the contact between points 9 and It], breaks away from its contact with point I0.

Figure 2 shows more in detail the arrangement of the switch. An inert gas at low pressure, for example neon at 8 mm. is introduced into the container l3 which is a sealed unit embodying the switch. This container may be made of glass, metal or the like. If it is made of metal, the lead-in wires must be properly insulated therefrom. The lead-in wires l4, and I5 are coated with an insulator I6, and H to confine the discharge to the vicinity of the bimetallic strip.

In operating, when a voltage of say 220 volts is placed across points 9 and I0 in the switch, a discharge takes place across these points. This discharge is concentrated at the top of the points, by covering all but the top with an insulating material, say aluminum oxide. This concentrated discharge so heats the bimetallic strip II as to cause it to expand and close points 9 and Ill. This bimetallic strip is made of two metals say copper and iron with different co-efiicients of expansion. The resulting short-circuit causes the electrodes 3 in the lamp l to heat up and the bimetallic strip H to cool, these two efiects of the short-circuiting being timed so that the electrodes will be sufliciently heated to start the discharge at approximately the same time that the bimetallic strip has cooled to a point where it breaks away from point Hi.

When the discharge takes place after the electrodes have been heated sufiiciently, the lamp starts and as a result the voltage across the switch drops to a point too low to start another discharge across the points of the switch.

In order that the switch may not start at too low a voltage, thermionically emissive coatings should be avoided on the electrodes. In that way, a switch which will not start at say, volts, but will start at 200 volts is provided.

What I claim is:

A discharge lamp starting switch comprising: a sealed glass container; an atmosphere of inert gas at low pressure in said container; a lead-in wire extending into the atmosphere in said container; a bimetallic strip attached at one end to said lead-in wire at right angles thereto, and having its other end free; a second lead-in wire extending into said atmosphere and placed in a position toward which said bimetallic strip will bend when heated and near enough to the normal position of the free end of said strip to permit a discharge to start in the atmosphere between said strip and said second lead-in wire at a voltage below 220 volts, and a coating of solid insulating material over each of said lead-in wires to confine the discharge to the vicinity of the bimetallic strip, said lead-in wires and said strip being free from thermionic coating materials so that a discharge will not start in the device at a voltage below 110 volts.

HENRY J. MCCARTHY. 

